THERMODYNAMICS: CHE1201
By Joseph Ddumba Lwanyaga; Bsc. AGE,
MSc. ESE
+256-706312211/777824770
jlwanyaga@gmail.com,
jdlwanyaga@eng.busitema.ac.ug
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Grading
• Assignments (2), and project: 20 marks
• Tests (at least one): 20 marks
• End of semester examination: 60 marks
Course rules and regulations
• Attendance to lectures and class exercises is compulsory
• Checking of attendance at the beginning of lectures may be done
• Come to lectures about 5 minutes before starting time
• Assignments plagiarism and tests and/or examination malpractices
will be highly penalized.
• Switch off or turn your mobile phones to silence mode during
lectures.
Course Objectives
• To provide students with the basic principles of thermodynamics relevant to
Engineering processes.
• To state and understand the laws of thermodynamics
• To apply the knowledge in the analysis of thermo systems.
Course Content
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Basic concepts
Equation of state and ideal gases
Specific heat capacities and perfect gases
Zeroth law of thermodynamics, temperature and its measurement
Heat and work; determination of work for various paths/processes
First law of thermodynamics as applied to closed and open systems
Steady flow and the continuity equation
Application of first law to common systems
Steam tables and the working fluid
Second law of thermodynamics and entropy
Application of the second law to heat engines, Refrigeration and heat pumps
Otto, Dual, Atkinson, Joule (Gas turbines) and diesel cycles
Combustion equations and chemical equilibrium
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INTRODUCTION
 Thermodynamics; defined as the study of energy in its various forms and
transformations and the interaction of energy with matter.
Concerned with interactions between the influence of the system on its
surroundings and vice versa
Classical and Statistical Thermodynamics
 Classical thermodynamics  Macroscopic approach to the study of
thermodynamics that does not require a knowledge of the behaviour of
individual particles of the system.
 Statistical thermodynamics  More elaborate approach, based on the
average behaviour of large groups of individual particles
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Some Applications of Thermodynamics
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Thermodynamic system
 A definite quantity of matter bounded by some closed surfaces
 Closed surface is referred to as the system boundary.
 Anything outside boundary is referred to as the surrounding
 Boundary can be real or imaginary.
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Closed and Open systems
Thermodynamic systems
Closed system
Open system
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Thermodynamic properties
 A property is any macroscopic observable characteristic of a system  Can be
categorized as intensive or extensive.
 Thermodynamic state described by specification of two or more values of
thermodynamic properties
Intensive properties
 Properties that are independent of the mass and are definable at a point in a
substance  value of the intensive property will be the same for each point in
the substance if the substance is uniform and homogeneous.
Examples  temperature, density, pressure, coefficient of viscosity, etc.
Extensive properties
 Properties of a system whose value for the entire system equals the sum of the
values for the component parts of the system or are properties that depend on
the total mass of substance under consideration.
Examples  enthalpy, internal energy, volume, mass, etc.
 The ratio of the extensive property of the system to the total mass of the
substance is referred to as the specific property.
 The total extensive property value of the system is always represented by a
capital letter e.g. Enthalpy [H] while its specific property value is represented by
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a lower case letter e.g. specific enthalpy [h].
Homogeneous substance
 A system is said to be homogeneous if the specific values of its properties are
the same at all points in the system.
Heat
 Form of energy which can be transferred from one body to another of lower
temperature by virtue of the temperature difference between the bodies
 Heat is a transient energy whose rate of transfer is proportional to the
temperature gradient
Sensible Heat
 Refers to that heat that causes a temperature change within a system. Sensible
heat is often given as;
Cp – Thermal capacity at constant pressure [kJ/K or J/K]
Cv – Thermal capacity at constant volume [kJ/K or J/K]
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Thermodynamic Processes
 A change in the state of a system or change in properties of a system
 The word “iso” is normally used to identify the property constant during a
certain process.
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Isothermal – constant temperature
Isobaric – constant pressure, 1 bar = 1*105 Pa
Iso-volumetric (Isochoric) – constant volume
Isentropic – constant entropy
Adiabatic – no heat exchange with surroundings
Isenthalpic – Constant enthalpy
Cyclic process
 A process that takes place in such a way that its initial and final states are the
same
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Quasi – Static process
 A process which occurs in such a way that at every instant the system departs,
only infinitesimally from an equilibrium state
 All the states through which a system passes during a process can be
considered as a succession of equilibrium states.
 Quasi –meaning almost, static meaning infinite slowness. Thus quasi-static
process is infinitely slow transition of a system. Infinite slowness is the
characteristic feature of a quasi-static process . A quasi-static process is a
succession of equilibrium states. It is a reversible process
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Quasi – static process cont’d
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Equilibrium
 Thermal equilibrium - A system is said to be in thermal equilibrium if there is no
temperature imbalance either within the system or between the system and its
surroundings
 Chemical equilibrium - A state attained by a system in which all possible
chemical reactions have ceased.
 Mechanical equilibrium - There are no unbalanced forces present either
internal to the system or between the system and its surroundings
Thermodynamic equilibrium
System is in thermodynamic equilibrium if it has attained mechanical, chemical and
thermal equilibrium concurrently
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Steady flow
 This is when the mass entering the system per unit time is equal to mass leaving
the system per unit time.
Zeroth Law and Temperature measurement
Zeroth law  When two bodies are in thermal equilibrium with the third body,
then the two bodies are also in thermal equilibrium with each other.
 Forms a basis of temperature measurement
Temperature measurement
 The zeroth law provides the basis for the measurement of temperature.
 It enables us to compare temperatures of two bodies A and B with the help of a
third body C and say that the temperature of A is the same as the temperature
of B without actually bringing A and B in thermal contact.
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Zeroth Law and Temperature measurement cont’d
 Thermometric property is the property that changes uniformly with
temperature that is used to measure temperature
Examples of thermometers
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EMPIRICAL TEMPERATURE SCALES
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Method in Use Before 1954
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Method in Use After 1954
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REVERSIBLE PROCESSES
 A reversible process is one that can be reversed without leaving any resultant
change in either the system or the surroundings
 A reversible process can be reversed without leaving any resultant change in
either the system or the surrounding  It is possible to change the direction of
the process without leaving any resultant change(s) within the system or
surroundings.
 It is an idealization. All actual processes are irreversible and approach the
reversible process only in special cases.
Criteria for reversibility
 The process must be frictionless
 Difference in pressure between the fluid and its surroundings during the process
must be infinitely small
 Difference in temperature between the fluid and its surroundings during the
process must be infinitely small
Note - All reversible processes are quasi – static but the reverse is not true
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Equations of state
 Two forms of equations of state of gas
v – specific volume [m3/kg], V – Volume [m3], R – gas constant [J/kgK], P –
pressure [Pa], T – Temperature [K], m – mass [kg]
n – number of moles, and - Molar gas constant [J/molK]
 The number of moles of gas can be computed as;
Relationship between R [J/kg.K] and
[J/mol.K]
From,
Comparing this with the expression
gives;
RmmCO2 = 44 g =44 *10-3 kg  RCO2 = 8.314/44*10-3 = 189 J/kgK
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Determination of work done during a volume change
 Consider a gas contained in a cylinder, during a given process the piston moves
from point 1 to point 2 resulting in the volume change from V1 to V2
 If the Force, F, causes the piston move through a small distance, dl, then work
done is;
 If the cross sectional area is A, then by definition of pressure;
 Therefore, the total work, W, can be computed by integrating between the states 1 – 2;
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Work done during some common processes
Isochoric process
Constant pressure process
A process with a hyperbolic equation e.g. Isothermal process
Polytropic processes
 These obey the equation;
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Work done during some common processes cont’d
Note;
 Using the equation PV = RT, it can be proved that the polytropic processes also
follow the equations;
Adiabatic processes
 For adiabatic processes, n =  = cp/cv
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Specific capacities
 Specific heat capacity at constant volume, cv is the change in internal energy per
degree temperature change for a constant volume process
Internal Energy, U
 The energy associated with the molecular motion of the substance.
 Internal energy differs from heat and work in that heat and work are transient
energies where as internal energy is a property of a system.
 These molecules have kinetic energy due to their translation, rotational and
vibratory motions and potential energy due to the intermolecular forces of
attraction which account for the system’s internal energy.
Enthalpy, H
 Enthalpy is the total thermal energy of the system.
 Can be computed as
 On a unit mass basis, specific enthalpy;
; u – specific internal energy
[kJ/kgK] and v – specifc volume [m3/kg]
 From the definition of cv,
 Specific heat capacity at constant pressure, cp is defined as the change in enthalpy per
degree temperature change at constant pressure.
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Specific capacities cont’d
 cp and cv for an ideal gas are functions of only temperature
and
 For a real gas, cp and cv vary with temperature but for most practical purposes, a
suitable average may be used.
 A perfect gas is an ideal gas whose values of cp and cv are constant for all
pressures and temperatures.
For a perfect gas;
; therefore,
; hence,
Relationship between cp and cv
From
,
, and by use of the gas equation;
, hence;
, putting
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